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Climate Hustle

SkS Analogy 10 - Bathtubs and Budgets

Posted on 12 October 2017 by Evan, jg

Tag Line

Adding 101 gallons to a 100-gallon bathtub causes it to overflow, even if added slowly.

Elevator Statement

No matter how slowly a bathtub is filled, adding more than 100 gallons of water to a 100-gallon bathtub causes it to overflow. This principle is clear, obvious, and one we encounter every time we take a bath.

Similar to the finite volume of a bathtub, Earth’s atmosphere has a finite volume. Because Earth’s atmosphere has a fixed volume, human emissions of greenhouse gases (GHGs) are increasing the atmospheric concentration of CO2, because we keep adding GHGs into this closed system, similar to running water into a bathtub.1 The concentration of CO2 does not depend on how rapidly we add GHGs to the atmosphere, but only on the total amount added.2 Lowering emission rates is important for improving the air quality in a large city, but carbon emission rates are meaningless for determining the global warming we will eventually experience due to a revved-up greenhouse effect: only the total amount emitted matters.3

Climate Science

The atmosphere has a budget of carbon it can accept to keep overall warming below a certain level, and the bathtub in this analogy is intended to be a visual representation of such a budget. Although scientists do not know with certainty how much the climate will warm for a doubling of CO2 (the so-called climate sensitivity), a climate sensitivity of 3°C/doubling of CO2 (see Ocean Time Lag)4 is consistent with the warming observed since the 1970’s, and is mid-range in the IPCC estimates that range from a low of 1.5 to a high of 4.5°C. Using a climate sensitivity of 3°C/doubling of CO2, a rough guide of the carbon budget corresponding to a particular level of warming is as follows5

•    350 ppm CO2 = 1°C warming (a warming we can live with, see
•    400 ppm CO2 = 1.5°C warming (things get worse for an increasing number of people)
•    445 ppm CO2 = 2°C warming (dangerous warming, but the best we can hope for)6 

      2°C warming is a guardrail beyond which changes become catastrophic

•    560 ppm CO2 = 3°C warming (really bad: and positive feedbacks accelerate)
•    700 ppm CO2 = 4°C warming (To be avoided at all costs)7

This means that there is a set amount of carbon we can emit into the atmosphere to keep the global average temperature below specific target temperatures. Emission rates are meaningless in this context. It is only the total emitted carbon that controls the ultimate warming.

However, emission rates are important for two other reasons.

  • The ability of species to adapt to a warming world decreases with increasing rate of warming.
  • Slowing the rate of warming buys us additional time to bring low-carbon power generation online before we exceed the carbon budget for staying below 2°C.

As the world comes out of an ice age the Earth warms about 5°C over 10,000 years, so we know that species currently present on Earth are adapted to that rate of change. The current rate of warming of about  2°C per 100 years is far in excess of natural cycles, and many species will likely disappear, even if we stabilize the warming at 2°C. Anything we can do to slow down the rate of warming will help species adapt and buy us needed time to implement solutions.

However, the core, long-term problem remains the total carbon emitted into the atmosphere, and not the rate of carbon emissions, because assuming that we are able to stabilize the temperature at 2°C warming (which implies that net carbon emissions drop to 0 at that point), 2°C warming will still imply multi-meter sea level rise, which will occur over millennia, and will require costly mitigation strategies for coastal communities.

The current level of CO2 in the atmosphere is already causing problems for many people, and the fraction of the Earth’s population experiencing climate-change-related stress will increase with increasing CO2 concentrations. The "bathtub" has been rapidly filled by developed nations, so it is reasonable that developed nations lead the efforts to stop the carbon buildup in the atmosphere.

The problem with talking about carbon budgets and motivating action needed to keep our total emitted carbon within a 2°C budget is that there is a delay between cause and effect. Specifically…

  • Even though CO2 levels are now higher than they have been in millions of years, because of the time delay for this warming to be manifested in the atmosphere, many people don’t yet perceive GHG emissions as a problem (problem of communication and trust in the scientific community).
  • Even if we perceive current warming as a problem for people in developing countries, in the developed countries we depend on CO2 emissions to maintain our lifestyles. Dealing with global warming means an uncomfortable adjustment to our lifestyle (problem of willpower).

And there is perhaps a third problem with comprehending the consequences of blowing a budget. People in “developed” countries live in an age of instant credit, refinancing, bankruptcy, welfare, so many variations of handouts and financial forgiveness that it seems that there is always somebody, something, or some kind of safety net that will catch us. The concept of no safety net is foreign to people living in affluent societies. For all intents and purposes there are no natural safety nets that will counteract our GHG emissions.8 At current emission rates that are increasing CO2 at a rate of 2 ppm/year, we will blow past the budget for staying below 2°C warming within 20 years.9 The only possibility for avoiding 2°C warming is for humans to alter their behavior and reduce energy use while we bring low-carbon energy sources online. The Paris Accord is one attempt to motivate governments to move in this direction, but individuals should also move on their own to reduce personal carbon emissions. There simply is no time to waste in waiting for governments to motivate action.

Negative-Emissions Technologies

Every year that we fail to reduce energy use and reduce carbon emissions, we increase the probability that we will blow past 2°C warming. Realizing that our current emissions trajectories will take us past 2°C warming, and yet wanting to maintain a semblance of hope without undue imposition on people in the developed countries, most emission scenarios presented by climate scientists for staying below 2°C global warming rely on negative-emission technologies that allow us to emit now and remove CO2 later. Kind of like the financial equivalent of buy now pay later. The problem, however, is that these negative-emissions technologies have only been demonstrated at the pilot scale, and have not been proven at the scale needed to meaningfully counteract GHG emissions. A good read on the subject is Kevin Anderson, or you can watch him as well. How easy is it to remove cream and sugar from your coffee once stirred in? How easy will it be to suck CO2 out of the atmosphere at a rate that will counteract the current, massive emission rates?

Is a 3°C target more reasonable and achievable?

For those who see a 2°C target as too ambitious, and prefer a longer-term approach of focusing on 3°C as a more attainable target, it is important to note that we may not have an option to stop the warming at 3°C. By that point positive feedbacks may drive the temperature higher, no matter what we do. There are large uncertainties about how the climate will respond as global temperatures increase, but natural feedbacks will certainly increase with increasing warming, making our emissions reductions less effective at controlling global warming as the planet continues to warm. There is the additional concern that although an increase from 2 to 3°C seems like a small step, in fact it represents significantly increased ocean acidification, increased storm intensity, increased sea-level rise, and most of all, significantly increased uncertainty about our ability to put the brakes on at all.10

This is why there is an urgency to meeting a 2°C target. A carbon budget for staying below 2°C is the last carbon budget for which there is a consensus among scientists that we have a reasonable expectation of controlling our own destiny. Beyond that warming, in addition to escalating negative effects, it is unclear how much control we will have over the climate.

No matter how much we justify our need for fossil fuels, continued consumption will lead to only one result: continued warming to … and then beyond the danger point. If you have not done so already, please read the NAS booklet on Climate Change: Evidence and Causes and then determine how you can begin/continue to cut back your use of fossil fuels. Let your elected officials know how you feel.

If you've read this far, you must be hungry for more detail. Check out Andy Skuce's article on the subject: Are we overestimating our global carbon budget?

Is it too late?

There is a growing realization that holding warming to 2°C warming may not be possible (see Glen Peter's excellent summary on this topic). Does this mean it’s too late and we should just give up? If you are driving a car and you suddenly realize you are going to run into a brick wall, no matter what you do, at what point is it “too late” to put on the brakes? At the point you put on the brakes you will avoid something worse. So even if it is too late to stop the warming at 2°C, remember that these are just numbers, there is uncertainty about the effects associated with these numbers, and that we will always avoid something worse later, by taking action now.




1. The difference between adding CO2 to the atmosphere and adding water to a bathtub is that CO2 added to the atmosphere has a negligible effect displacing air, whereas water added to a bathtub displaces all of the air previously in the bathtub. The point of the analogy, however, is to emphasize that to keep warming below the 2°C target set by the Paris Accord, there is a set amount of carbon we can emit before we exceed 2°C of warming, and the bathtub is intended as a visual representation of that budgeted amount of carbon.

2. Bathtub analogies have been formulated where water runs out of the drain as it enters from the faucet. The idea is that the natural system has sources and sinks, and that the rate at which the bathtub fills up is the difference between the sources and the sinks. In such analogies human emissions cause the inflow to increase, so that the human contribution is the difference between a large inflow and a large outflow. In this analogy the drain of the bathtub is plugged, so that the inflow represents the entire human contribution to the buildup of greenhouse gases. Therefore, in this analogy shutting off the faucet represents reducing net human greenhouse gas emissions to zero.

3. It is well known that land and ocean currently absorb roughly 50% of the CO2 that we emit. Emission scenarios account for this, so that when discussing how much CO2 we can emit to stay below a particular level of warming, the uptake by natural systems is accounted for. One way to assess the net effect of how well we're doing to reduce CO2 emissions is to look at the rate of CO2 increase per year, because the measured increase includes the difference between the CO2 emitted and the CO2 absorbed by natural systems. The problem, however, is that as the earth warms, the amount of CO2 taken up by natural systems may decrease, reducing the amount of CO2 we can emit to stay below target temperature levels. See Andy Skuce's excellent article on this issue.

4. 3°C increase of global average temperature for a doubling of CO2 concentration compared to the pre-industrial level of 280 ppm.

5. Dumping a fixed amount of carbon into the closed system represented by the atmosphere results in a measurable amount of CO2 in the atmosphere, which is quantified as molecules of CO2 (i.e., parts of CO2) per million molecules of air (ppm).

6. (PDF download) Hansen et al. state that 2°C warming could be dangerous.

7. (PDF download) Turn Down The Heat: Why a 4°C Warmer World Must be Avoided.

8. In the physical world there are “safety nets” of sorts, systems that maintain/restore balance, referred to by scientists as thermostats that maintain Earth’s climate within habitable bounds, but these processes act far too slowly to counteract the rate at which we are dumping CO2 into the atmosphere. Kind of like comparing the rate of evaporation of water from a bathtub compared to the rate at which it's being filled. The thermostats that control CO2 levels in the atmosphere require 10's to 100's of millennia to restore/maintain balance.

9. The CO2 concentration we will reach and the temperature we will lock in is a bit more complicated than the simplistic statement of multiplying 2 ppm/year x 20 years to say that we will be at 445 ppm (or thereabouts) in 20 years, because if we were to magically reduce our emissions to 0 after 20 years, the CO2 levels would decrease thereafter to a new equilibrium point, determined by the ability of land and oceans to absorb some of the CO2 we emit. For an interesting read on this subject that delves into more detail about stabilization dynamics, see Andy Skuce’s article Global Warming: Not Reversible, But Stoppable. Because CO2 emissions are controlled by many factors related to population, rise of affluence in the developing countries, deforestation, etc., I have assumed in my simplistic calculations that a reasonable expectation is that for the next 20 years we more or less maintain current emission levels. Whether this is optimistic, pessimistic, or realistic depends on how we respond to the call to action to reduce emissions. Realistic extrapolations of current trends are at best, flat. Getting our CO2 emissions pointing downward is a work in progress.

10. I do not have a good reference stating that warming to 3°C will cause uncontrollable feedbacks, but scientists often verbally state this in talks. A good source that infers the probability of uncontrollable feedbacks at 3°C warming is from Hansen et al., where they state "Cumulative emissions of ~1000 GtC, sometimes associated with 2 degrees C global warming, would spur “slow” feedbacks and eventual warming of 3-4 degrees C with disastrous consequences." The implications are that if we target warming for 2°C, and slow feedbacks take us to 3-4°C, then targeting warming for 3°C will likely activate feedbacks that will take us past 4°C, a warming that climate scientists say must be avoided at all costs (See footnote 7 above).


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Comments 1 to 37:

  1. Excellent discussion of 'climate accounting 101'.  Regarding your example of when to hit the brakes as we approach a cliff whose bridge is out: Rep. Lamar Smith has said its arrogant to predict what the climate will be in a century.  That's like claiming its arrogant to say that the bridge is out based on your looking forward.  Why does Smith not think its out?  Because he's looking backward, and you've been driving over flat country for as far back as the eye can see.  He therefore assumes flat country is ahead of you.  It's important to tell the 'Smith's of this world that just because he thinks its arrogant to make a prediction of the future status of the road based on looking at it,  it doesn't mean he hasn't made a prediction.  He may just not be aware that he has made one.  Without quite realizing it, he thinks the future will be flat as a pancake, because the past has been, and that is a prediction.  As it happens, a more arrogant prediction than looking forward and telling folks what you see ahead of us.

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  2. Very well written and hard to fault, with foolproof, convincing, informative analogies.

    Lamar smith saying its arrogant to make a prediction does indeed show lack of self awareness that we make predictions all the time anyway. In fact various studies in economics show humans make decisions on virtually everything by mentally weighing probabilities of various events happening in the future. Science simply informs us on whats most likely to happen in the future in a rigourous way, better than gut feel etc or assuming things will continue as in the past. I would say its extremely arrogant of Lamar Smith to ignore science.

    We can extract some of the water in the bathtub a little with man made carbon sinks. The paris accord requires 'net' zero emissions by 2050 so allowes for carbon offsets like this. Both tree planting and soil sequestration of carbon through better farming systems have potential as offsets from the IPCC reports. 

    However there are some big challenges. Both are somewhat slow processes to implement in a practical, educational and political sense, and time is not on our side, so the primary goal has to be to reduce emissions at source, with strengthened carbon sinks to help mop up some emissions.

    Tree planting is problematic, because suitable land is limited, and the quantity of trees needed to make a huge difference is vast when you do the maths. The temptation to fell the trees prematurely is going to be huge. 

    I see the most plausible thing as rigourous development of carbon sinks of various types could potentially offset some of the difficult  to reduce emissions like aviation emissions, and perhaps some inductrial emissions but thats about all. Still that would help solve a difficult problem.

    Of course over more extended time frames man made carbon sinks may also help draw down excess CO2 in the atmosphere.

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  3. If we look backwards as it has been suggested by ubrew12@1 that Lamar Smith is apparently doing, we still see the climate warming at a measured rate of 2C/100 years (see Analogy 4). Thus, projecting forward with a linear view derived from the past still spells trouble.

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  4. In the cartoon, it should be "never too late".

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  5. Thank you Digby for your correction. And to think I once called myself an editor.

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  6. I just noticed the other embarassing mistake. "When is it too late the hit the brakes" should be "When is it too late to hit the brakes"

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  7. Never mind, Evan.  As a retired technical writer, I know just how difficult it is to rid even the simplest document of all typos and silly mistakes.

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  8. Excellent reduction of the challenges to gobal efforts to effect gobal climate change: "problem(s) of communication and trust in the scientific community" & "problem(s) of willpower."

    I also like the implicit recognizitonthat the only significant engineering problem left is the development of effective carbon removal technology by omitting any debate re: the feasability/reliablity of low-carbon energy systems.

    Becuase of the uncertainty and ethical dilemma of "betting" on future development of direct atmospheric carbon removal technology, I would be interested in seeing more information on the potential impact of forest conservation a la the UN-REDD program to "reduce forest emissions and enhance carbon stocks from forests while contributing to national sustainable development."

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  9. Tunnelly,

    You said, "I also like the implicit recognizitonthat the only significant engineering problem left is the development of effective carbon removal technology" 

    Actually that part of it is done. We can do it and it is feasible and mature technology and the case studies have been done to prove it feasible at scale in the field. Not only feasible but actually highly profitable. 

    The problem has nothing to do with technology but rather the many billions of dollars being spent to prevent it from being implemented.

    Liquid carbon pathway unrecognised

    Farming a climate change solution


    "If all farmland was a net sink rather than a net source for CO2, atmospheric CO2 levels would fall at the same time as farm productivity and watershed function improved. This would solve the vast majority of our food production, environmental and human health ‘problems’." Dr. Christine Jones

    I wrote several whole essays about it both here and at quora. One of them was recently picked up by RedPlanet and published.

    Can we reverse Global warming?

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  10. CO2 levels were higher throughout most o of Earth's history. Temperatures have been higher in the past as well and life thrived. CO2 levels of 1000 ppm are ideal for greenhouses and agriculture has benefited from increasing CO2 levels. I saw a presentation where none of the CO2 models accurately predicted temperature as the CO2 levels have risen. NASA just admitted that sea levels have fallen. Too many natural factors such as solar sunspot cycles, orbital cycles, climatic oscillations, accrurately understanding the carbon cycle, and historical climate change has been left out in the AGW proponents rush to solely tie CO2 levels temperature fluctuations.

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    Moderator Response:

    [JH] Blatant sloganeering sipped.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  11. cjones @10

    I disagree completely, and you cite no sources of research information, so have no credibility.

    "CO2 levels were higher throughout most o of Earth's history."

    Just a false empty assertion with no evidence provided, plus bad spelling. CO2 levels are currently considerably higher than at least the last 800,000 years as below.

    "Temperatures have been higher in the past as well and life thrived. CO2 levels of 1000 ppm are ideal for greenhouses and agriculture has benefited from increasing CO2 levels."

    The sort of life that thrived in higher temperatures was not necessarily the ideal sort of life actually. The temperatures we are heading towards are not good for crop production ultimately, and for human survival, and the rapid rates of change are greater than historically, and thus present particular problems with adaptation for all species. Higher temperatures also mean sea level rise and more intense storms. This is all covered in the last IPCC report, which is available online and easily googled.

    And humans dont live in glass greenhouses.

    "According to NASA sea levels have fallen...."

    For about two years, which is normal short term fluctuation due to natural variability, just as they have fallen for short periods like this scattered through the last 100 years, then increased again on each occasion after a couple of years in a pattern over time. The dominant trend over the last 100 years is rising sea levels easly seen if you google the jason topex satellite sea level rise data.

    "Too many natural factors such as solar sunspot cycles, orbital cycles, climatic oscillations,"

    Blah, blah, blah the denialist does his best to spread confusion and doubt straight form the corporate lobbying play book. All these elements have been researched in hundreds of research papers, and do not explain recent warming. Try reading this website starting with the list of "most used climate myths"

    I dont think the moderator is going to be happy with you somehow. 

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  12. cjones @10

    You got caught in the merchant of doubt minefield. I get it. They can be sneaky and have fooled many. But be sure that while yes indeed from time to time CO2 levels have been higher, it was certainly not a good thing. Actually it is associated with several mass extinctions.

    The logic fallacy of the merchants of doubt fallacy goes a little like this: CO2 was higher in the past, and life thrived in the past, so current higher CO2 levels will make life thrive even more.

    The problem is we also had many mass extinction events in the past too. And sure enough if we look closely at the fossil record, we find that the mass extinctions mostly happened either directly or indirectly from this high CO2 levels when they went on runaway feedbacks for various reasons.

    The evidence is pretty clear actually, although still debated and not certain, it is pretty likely. Far more likely than runaway CO2 being a good thing.

    Great Dying 252 million years ago coincided with CO2 build-up

    Timeline of a mass extinction

    Ocean acidification and the Permo-Triassic mass extinction


    and not only the permian extinction. It is actually a common theme in many mass extinction events.

    Doubling Of CO2 Levels In End-Triassic Extinction Killed Off Three Quarters Of Land And Sea Species


    CO2 levels and mass extinction events

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  13. Fox news tends to down play the risks of global warming, ocean acidification, and climate change. However, here is a quote from Fox news.

    "Rising sea levels caused by climate change is expected to exacerbate storm surge flooding."

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  14. Nigelj @11 , it is bold of you to oppose the ideas of Cojones1 (at post #10 ).

    Think back 80 years of history, and you will see how the Gish Gallop of ideas of Cojones1 brought about some major changes in Europe especially.  If I recall correctly, the well-known Allied soldiers' marching song also mentioned Cosmoswarrior1 as having something similar.

    And thank you for your comments, RedBaron @12 . . . though it is distinctly ironic to see the RedBaron flying against the Central Powers of Cojones1 .

    Evan @13 , it is certainly tempting to think "the tide has turned" at FoxNews, and that they will in future be reporting truthfully on Global Warming matters.  But their track record is discouraging, in that regard.

    Yes, a fine Gish Gallop of ideas @10  . . . indeed a bathtub full of them!  But an overflowing bathtub seems to have failed to bring any Archimedean enlightenment to Cojones1 .

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  15. Eclectic@14. Thank you for your comments. My point in quoting Fox news was certainly not to suggest the tide has turned at Fox news, no pun intended. My point was to counter the misinformation of cjones1@10 that "sea levels have fallen." Apparently it is so obvious that they are riaing that not even Fox news suggests they are falling.

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  16. cjones1 @10

    What made you think you could get away with your gish gallop of garbage at a website run by climate scientists and frequented by a large number of science-literate people?

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  17. Eclectic@14. Thank you for your comments. My point in quoting Fox news was certainly not to suggest the tide has turned at Fox news, no pun intended. My point was to counter the misinformation of cjones1@10 that "sea levels have fallen." Apparently it is so obvious that they are riaing that not even Fox news suggests they are falling.

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  18. Nigelj@2 Biochar has been suggested before but few on this list have taken it up, partly because it requires some info.

    However, creating Biochar by feeding Cows, Charcoal, needs no explanation. According to a quick Google search there are 3.2+ Billion cows on our planet, and the demand for their meat will not stop any time soon, - in Australia, there are 28 Million, - outnumbering the people.  If you feed a cow between 200 and 400 gms of charcoal per day, it becomes heathier, requires less feed, puts on more weight and is more placid, - see

    so 300 gms (a conservative average) times 3.2 Billion (+) per day, gets app. 1 kg per 3 cows, so app. 1 billion kgs per day, fed to them with their molasses, and then shat out as Biochar, enzymes and all, then buried by the ubiquitous dung beetle, there to enrich the soil and allow it to sequester more carbon in the process, - win,win. 

    I realize that 365 billion kGs of carbon/year is not enough, although it is more than that in terms of carbon dioxide, -  times 3.5+  but all those figures are conservative, do not take into account all the other meat etc. animals that human beings have been blessed with, nor the sequestration possible with that carbon stimulating the soil, nor that taking charcoal for flatulence is well known to humans, so apparently the cows do not fart much methane, - don't know if it affects their burping..

    Perhaps there could be a Charcoal tax rather than a carbon tax? - could be politically more acceptable. :)

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  19. GeoffThomas@18, thanks for your interesting post. I was not aware of this, and will certainly study this more. There are so many angles to climate change, and whether or not it is as easy as you suggest (feeding charcoal to cows to sequester carbon), it certainly is informative to see additional, creative contributions to the "silver buckshot" we need to get ahead of this problem.

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  20. Evan @19, yes it is an interesting aspect, although I live in a cattle area and those farmers tend to be conservative. I am not giving up however.

    Another mob doing research is Ithaka institute in Germany,

    In the credits for the above u-tube is a Stephen Joseph, he is doing some amazing research on the more complex aspects of Biochar, -cat-ion exchange enabling etc, a researcher well worth watching.

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  21. Geoff Thomas, thank's for the information on biochar.

    I have to confess I didn't know anything much about it, and had to go a google and read a couple of articles, which totally support what you say. It appears to have a whole range of benefits, and more to the point adequately proven benefits. This alone suggests its an obvious thing to promote.

    Its interersting and relevant because my country is hugely dependent on diary farming.

    I'm a little bit interested in the use of carbon sinks in the wider sense to mop up emissions. I think Evan is right that storing carbon underground and geotech approaches have so many obvious problems, and can't be counted on. It's one thing to be optimistic about technology when progress is clearly being made and plausible, like battery technology, and another thing to have delusional faith in schemes that even commonsense should tell you are implausible or not cost effective.

    But I think natural carbon sinks have some value, and biochar is part of this. I think its probably a case of promoting a combination of things from biochar, to tree planting, to better soil management as various  other people talk about on this website.

    I think its a case os 1) cutting emissions and 2) promoting natural carbon sinks. Carbon sinks wont do it alone, but will help mop up some emissions. I think its a slow process, but would deal with maybe the difficult aircraft emissions.

    However while trees have the most mass storage potential some real problems are clear. For example all these forest fires lately are probably linked to climate change, and  undermine this particular carbon sink, and theres evidence some forests are becoming net CO2 emitters, and theres limited land for growing trees. And demand for timber is huge.

    In contrast farming and soil management is just a change of methodology, not requiring more land. So it may have more practical potential in the longer term.

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  22. @GeoffThomas,

     You said, "I realize that 365 billion kGs of carbon/year is not enough, although it is more than that in terms of carbon dioxide, - times 3.5+ but all those figures are conservative" 

    Actually they are at least an order of magnitude too small, assuming the technique is used to it's full potential. That's because the true value of biochar is in jump starting the liquid carbon pathway by providing a habitat for AMF to get started, and AMF to all the heavy lifting when it comes to carbon sequestration. I had place a link in my previous answer, can we reverse global warming, if you scroll down you will find the technical brief on how it works.

    Technical Brief: The Liquid Carbon Pathway


    You are just counting the biochar, but in reality, managed properly, it's the glomalin and humic polymers that end up making the vast bulk of the carbon in terre preta. The biochar is just the scaffolding for the living biology that pumps carbon in the soil at a rate of 5-20 tonnes CO2e/ha/yr. Remember, all it takes is 8 tonnes CO2e /ha/yr if all the arable land in the world did this. (integrated in cases of crop and animal husbandry combined) So we are roughly talking about 1/2 the solution actually. (reducing fossil fuels use with solar wind and hydro being the other 1/2)

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    Interesting article highlighting problems of geotech engineering solutions to climate change. This includes problems of reflection of sunlight, and risks and problems of extracting CO2 through technical fixes, like altering ocean chemistry, and irrigating deserts to plant plant trees.

    I dont see how you can be clear on what the effects and risks are from some little isolated experiment over a small part of the atmosphere. This would not be sufficient to account for wide scale atmospheric effects you get in reality. Some of the ideas would also not be easily or quickly reversed, if they went wrong.

    We should stop emissions, and stay with more measured enhancements to natural carbon sinks that are a known quantity with low risks.

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  24. ubrew12:

    >>Without quite realizing it, he thinks the future will be flat as a pancake, because the past has been, and that is a prediction. As it happens, a more arrogant prediction than looking forward and telling folks what you see ahead of us.<<

    An excellent analogy/example and one I hadn't thought of.

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  25.>>Moderator Response:
    [JH] Blatant sloganeering sipped.

    Please note that posting comments here at SkS is a privilege, not a right. This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it. Thanks for your understanding and compliance in this matter. <<

    Moderator: I respectfully can't agree that the sort of posts to which you append this standard reply are not helpful: if the poster reads replies from scientifically literate people surely there is a chance that he might be educated?

    In addition, looking back over the months, this "standard" reply does allow the deniers to claim that all sceptical (in their terms)  debate is quashed.

    Just a thought.

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    Moderator Response:

    [JH] We will continue to moderate comments posted on this website in accordance with our standard practices. If a comment is not in compliance with the SkS Comments Policy it will be appropriately dealt with. 

  26. Wol @25 , just a thought from me :

    In actual practice at SkS, you will find that serious/intelligent "sceptical" debate is encouraged.   That said, there is in fact very little serious/intelligent "sceptical debate" to be found anywhere let alone in the columns of SkS !   Sure — unintelligent and/or non-serious [ = trolling ] debate abounds . . . and deserves to be snipped [here].  

    The self-called "skeptics" have such a low level of truthfulness, that they would (and do) bad-mouth SkS at every opportunity.   Nothing whatsoever would be improved by giving them a free rein here at SkS.  Quite the contrary, indeed !!   SkepticalScience would be overrun & trashed by posts oozing malice & idiocy.  (Just observe the current fate of most public website comments columns that lack proper moderation monitoring! )

    Wol, you are far too kind-hearted.  I respectfully counsel you to ignore the delicate sensibilities of denialists/"skeptics".   Denialists won't be convinced by anything, to change their minds to a sane realistic attitude to AGW.


    The only moderation plea I have is for Moderator comments to be kept in the traditional "green boxes" where they are easy to see, and are not half-buried in the text of regular posts.

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  27. Some statements in the article seem to be inaccurate. "Earth atomospere has a finite volume". Does the author mean all the atmosphere which nominal borders are determined by amount of gases retained by Earth's gravity? Rather it's lower layer of the troposphere containing most of greenhouse gases. However, in this case the borders of the lower layer are also conditional because of uneven height distribution of different GHGs according their molar masses (for example, methane and CFCs). 

    "We keep adding GHGs into this closed system". The system is not closed: CO2 dissolved in fresh and saline water, absorbed by vegetation. 

    About relationship between the "budget of carbon" and "overall warming". It would be correct within the framework of greenhouse effect theory, if CO2 is indeed the main greenhouse gas. However, water vapor is stronger greenhouse gas than CO2: Th.L.Brown, H.E.LeMay a.o. Chemistry. The Central Science. Pearson. Prentice Hall. 4th Ed. 2009, p.781. Zerenboren & Kilpinen estimated the contribution of H2O to greenhouse effect of ~2/3: According to another source "water steam accounts for 36-70% of greenhouse effect". Moreover, in IPCC list of long-lived (only!) greenhouse gases:                   the radiative forcing (rf) value of CO2 is only 0.63 of the total rf of all gases in the list.                                                                                         So, the contribution of CO2 in any case will be much less than 50%.          That's why analogies between atmosphere and a bathtub, as well as between CO2 in atmosphere and water in a bathtub seem to be doubtful.

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  28. aleks@27, thanks for some good points. Here are some responses.

    Regarding the atmosphere being a closed system, carbon budgets developed by the IPCC account for the fact that the oceans and biosphere absorb much of the emitted carbon. The reason why I refer to the year-on-year increase of CO2 is that the yearly increase is the net effect of emissions minus uptake by the oceans and biosphere. The fact that CO2 is increasing over 100 times faster than any natural cycles in the last several million years is evidence enough that we are essentially emitting into a closed system. That is, the natural removal rates cannot keep up with our emissions. Again, IPCC estimates account for the effect of natural removal mechanisms in determining budgerts that represent the amount we can emit into what is essentially a closed system to stay below a specific warming.

    Regarding H2O as a stronger greenhouse gas, yes it is. But the H2O increases in response to increases of CO2, and not independently. Again, IPCC estimates account for the fact that CO2 is the main driver and H2O simply responds. That is, the removal rates of CO2 are so slow, that we can easily build up CO2 concentrations by emitting more. This is not so for H2O. If we emit more H2O, it simply rains out in a few weeks. The only way to increase H2O concentrations is to increase the temperature of the atmosphere. Once temperature is increased by the CO2 emitted, then H2O increases as a response (i.e., positive feedback). The H2O increase for a given temperature increase is governed by the Clausius-Clapeyron equation.

    Therefore, CO2 is still the driver, and H2O merely responds.

    But thanks for your comments. It is good to get different viewpoints.

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  29. aleks@27, perhaps I should respond to your comments as follows. No analogy is perfect, and certainly the atmosphere is not a closed system in the strict sense as you point out. But the point I am trying to make is that whereas pollutants are regulated in cities because of the locally high pollution that can result from high emissions, once emission rates are reduced, the outside winds flush the pollutants out of the city. In contrast, the effect of CO2 in the atmosphere does not depend on the rate at which we emit, but only on the total amount, because CO2 slowly builds up, and there is no ourside source to flush the CO2 away. Once we raise the level in the atmosphere, we are stuck with this concentration for a very long time, until the sinks to which you refer slowly bring down the concentration. These sinks act so slowly (i.e., 100's to 1000's of years) compared to the time scales that we care about (the lives of our children and grand-children), that effectively we are emitting CO2 into a closed system: once we emit the CO2 we are stuck with it for the future we care about.

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  30. @ Evan #29,

    You said, "That is, the natural removal rates cannot keep up with our emissions."

    You are correct. But I would like to point out the primary land based rapid removal of CO2 back into the long cycle is 99% destroyed by agriculture. Even secondary pathways are by vast majority destroyed by agriculture. Of course the rate is 100 times faster than can be removed and the sequestration rate is woefully inadequate. It's basically by all intents and purposes destroyed and actually turned into an emissions source instead, with a few rare exceptions.

    Global Cooling by Grassland Soils of the Geological Past and Near Future

    Farming Claims Almost Half Earth's Land, New Maps Show


    Tallgrass Prairie--the Lost Ecosystem

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  31. Red Baron, I was reading carbon rich soil is some Australian grass lands go down 20 metres, which indicates the potential.

    But what do you make of this? looks ominous:


    "Soil will absorb less atmospheric carbon than expected this century, study finds". It appears to be saying potential is huge but its a slow process. Or is the study wrong or out of date?

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  32. RedBaron@30, thanks for the additional links. Interesting points you make about how much the natural cycles could be helping us.

    But my basic point is that whatever the land and oceans are doing to remove CO2, we are still building up CO2 at a net 2 ppm/year, which is disasterous. At this rate we are only about 20 years from the budget for staying below 2C. So whatever promises there are for using sequestration technologies, whether natural or artificial, we had better get busy using them. If modified farming practices can be used to sequester additional carbon, that would be great.

    Thanks for pointing out a side of the discussion that I know I have been overlooking.

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  33. Evan@28,29, thanks for detailed reply.                                                           About natural removal rates for CO2. Please, pay attention to the research by A.Ballantyne a.o. (University of Colorado)              

    The authors state that "natural carbon sinks that sequester the greenhouse gas doubled their uptake in the past 50 years".

    Reference to the Clapeyron-Clausius equation shows that you consider  water concentration change in the atmosphere only in relation to temperature. However, water emitted together with carbon dioxide at combustin of fuel in huge quantities. So, at burning of methane the yield of H2O is 2mole/mole CO2, for oil it will be slightly more than 1mole H2O/1mole CO2. Even coal contains about 6% H by mass. This is an additional evidence in favor of the significance of water vapor for the processes of heat exchange in the atmosphere.

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  34. aleks@33 Yes, H2O is a primary combustion product together with CO2. For "clean fuels" such as CH4, twice as much H2O is emitted as CO2. But the excess H2O just falls out of the system as precipitation. So the only increase of the steady-state H2O concentration is through the Clausius-Clapeyron equation, and is not due to direct emission of H2O. That is, the only way that the steady-state concentration of H2O can increase is if there is an increase of temperature first. Direct emissions of H2O do nothing to inrease to increase steady-state concentrations of H2O.

    Regarding uptake of CO2 doubling, I am not an expert in this area, but this number does not surprise me, and it does not make me feel better. Consider that for about 10,000 years during the Holocene that background CO2 concentrations were about 280 ppm. The fact that the concentration was stable means that sources and sinks were in equilibrium. Then comes the industrial revolution and we start to ramp up CO2. By the late 1960's the CO2 concetration had increased to about 325 ppm. This is an increase of 45 ppm above the steady-state value during the Holocene. The result is that the earth starts to absorb more CO2 to draw down the concentration and to try to restore balance. Now we are at about 405 ppm, or about 125 ppm above preindustrial, and about 3 times higher than the 45 ppm inbalance representative of the late 1960's. So it is not surprising that the rate of sequestration has doubled in the last 50 years, because the increase above preindustrial has tripled. Far from making us feel better, the fact that we are dumping such huge levels of carbon into the natural system represents a deviation from the steady-state balance we had for 10,000 years, and such a dramatic departure should make us worry about what effect this will have. Such as ocean acidification. We know some of the good benefits, but we may yet discover that there are other not-so-good effects lurking in the dark.

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  35. aleks@33, from the paper you cited, there is the following cautionary note.

    “What we are seeing is that the Earth continues to do the heavy lifting by taking up huge amounts of carbon dioxide, even while humans have done very little to reduce carbon emissions,” said Ballantyne. “How long this will continue, we don’t know.”

    The fact that the earth is absorbing large quantities of our emissions is great, but it has its limits. The fact that the offset of current CO2 compared to preindustrial is 3 times higher now than in the late 1960's but the authors say the uptake has only doubled may already be a sign that the uptake is slowing down. This is the nature of systems as they become saturated.

    We are digging up carbon and dumping it into the above-ground systems at a rate they are not accustomed to. The result will not be good. We need to start leaving the carbon below ground where it is, instead of trying to convince ourselves that either nature or our technology will find ways to put it back underground. Why not just leave it where it is?

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  36. Aleks @33, the university of bolder study is 5 years old now, and not representative of all studies. Uptake of natural sinks is difficult to determine and you need to look at all the research. Many other studies are more pessimistic especially more recent studies.

    For example the article below discusses research finding ocean uptake of CO2 has actually slowed since 2000 due to increasing acidity.

    The following article in Science Daily discusses research that finds soil sinks wont absorb nearly as much carbon over the next century as thought.

    I could go on with more. Natural sinks have their limitations and carbon dioxide draw down is basically a very slow process over millenia. This emphasises the need to cut emissions at source. We can enhance natural sinks a bit, but the potential is limited mainly by the slow process of impementation and slow uptake of CO2.

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  37. Aleks @33, yes water vapour is a greenhouse gas and associated with combustion of fossil fuels,  but you again miss the point. It mostly probably falls mostly as rain, but the simple fact is its intrinsically associated with increasing fossil fuel emissions and this water vapor is thus increasing and is another warming agent. The message: Stop burning fossil fuels.

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